Subsea fluid processing system with intermediate re-circulation

ABSTRACT

A fluid processing system is provided containing a pump and a fluid reservoir. The pump includes a casing, one or more pump stages, a pump inlet, and a pump outlet. The casing includes one or more slots, with at least one slot configured to extract at least a portion of a multiphase fluid flowing within the pump. The fluid reservoir encompasses at least a portion of the casing and is configured to receive and separate the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase. The fluid reservoir includes a re-circulation conduit disposed proximate to the pump inlet and a discharge device coupled to the re-circulation conduit. The discharge device regulates re-circulation of at least a portion of the extracted liquid phase to the pump via the pump inlet for reducing a gas volume fraction of the multiphase fluid being fed to the pump.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) fromProvisional Application No. 62/079,125 filed on 13 Nov. 2014, which isincorporated by reference herein in its entirety.

BACKGROUND

The present invention relates to fluid processing systems for deploymentin a subsea environment, and more particularly to subsea systems capableof handling production fluids characterized by high gas volume fraction(GVF).

Fluid processing systems used for hydrocarbon production in subseaenvironments typically include pumps configured to boost productionfluids from a subsea hydrocarbon reservoir to a distant storagefacility. Such pumps are typically designed to operate with productionfluids having relatively low gas volume fraction (GVF).

Generally, gas slugs occur due to flow instability of multiple phases ofthe production fluids. Such flow instability may occur in pipelinesdeployed for moving the production fluids. Eventually, these gas slugsmay enter the fluid processing systems and may cause rapid change in theGVF to higher values. Pumps receiving such production fluids with highGVF may be damaged thereby.

To protect the pumps from incoming gas slugs, a portion of a liquidphase of the production fluid may be re-circulated from a downstreamseparator to the inlet tank, where the liquid phase is mixed with theincoming production fluid before being fed to a pump. However, suchre-circulation of the liquid phase may result in overall pressure lossesto the system as the liquid phase at high pressure needs to be throttledto lower pressure before being fed to the inlet tank. Further, when thepressure is lowered the liquid phase may tend to flash (i.e. convertfrom a liquid phase to a gaseous phase) which may reduce efficiency.

Thus, there is a need for an improved fluid processing system forefficiently handling production fluids characterized by high gas volumefraction (GVF) and to regulate the GVF of a production fluid being fedto a processing system pump.

BRIEF DESCRIPTION

In one embodiment, the present invention provides a fluid processingsystem comprising: (a) a pump including a casing, one or more pumpstages, a pump inlet, and a pump outlet, the casing defining one or moreslots, wherein at least one of the slots is configured to extract atleast a portion of a multiphase fluid flowing within the pump, andwherein each pump stage comprises a diffuser and an impeller; and (b) afluid reservoir encompassing at least a portion of the casing andconfigured to receive and separate the portion of the multiphase fluidinto an extracted liquid phase and an extracted gaseous phase, whereinthe fluid reservoir comprises a re-circulation conduit disposedproximate to the pump inlet, and a discharge device coupled to there-circulation conduit and configured to regulate re-circulation of atleast a portion of the extracted liquid phase to the pump via the pumpinlet so as to reduce a gas volume fraction (GVF) of the multiphasefluid being fed to the pump.

In another embodiment, the present invention provides a method forreducing a gas volume fraction of a production fluid comprising: (a)introducing a multiphase fluid into a pump configured to increasepressure of the multiphase fluid, wherein the pump comprises a casing,one or more pump stages, a pump inlet, and a pump outlet, wherein eachpump stage comprises a diffuser and an impeller; (b) extracting at leasta portion of the multiphase fluid flowing within the pump into a fluidreservoir encompassing at least a portion of the casing via one or moreslots defined in the casing, wherein the fluid reservoir comprises are-circulation conduit disposed proximate to the pump inlet and adischarge device coupled to the re-circulation conduit; (c) separatingthe portion of the multiphase fluid into an extracted liquid phase andan extracted gaseous phase; (d) re-circulating at least a portion of theextracted liquid phase through the re-circulation conduit into the pumpvia the pump inlet by regulating a flow of the extracted liquid phasevia the discharge device; and (e) mixing the extracted liquid phase withthe multiphase fluid at the pump inlet so as to reduce the gas volumefraction (GVF) of the multiphase fluid being fed to the pump.

In another embodiment, the present invention provides a method oftransporting a production fluid comprising: (a) receiving a firstproduction fluid in an inlet tank and mixing it with a primer liquid toproduce thereby a second production fluid (multiphase fluid) having areduced gas volume fraction (GVF) relative to the first productionfluid; (b) introducing the multiphase fluid from the inlet tank into apump configured to increase pressure of the multiphase fluid and producethereby a compressed multiphase fluid, wherein the pump comprises acasing, one or more pump stages, a pump inlet, and a pump outlet, andwherein each pump stage comprises a diffuser and an impeller; (c)extracting at least a portion of the multiphase fluid flowing within thepump into a fluid reservoir encompassing at least a portion of thecasing via one or more slots defined in the casing, wherein the fluidreservoir comprises a re-circulation conduit disposed proximate to thepump inlet and a discharge device coupled to the re-circulation conduit;(d) separating the portion of the multiphase fluid into an extractedliquid phase and an extracted gaseous phase; (e) re-circulating at leasta portion of the extracted liquid phase through the re-circulationconduit into the pump via the pump inlet by regulating a flow of theextracted liquid phase via the discharge device; (f) mixing theextracted liquid phase with the multiphase fluid at the pump inlet tofurther reduce the GVF of the multiphase fluid being fed to the pump;and (g) transporting the compressed multiphase fluid from the pump to afluid storage facility via a fluid conduit.

DRAWINGS

These and other features and aspects of embodiments of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a subsea system in accordance to an embodiment of theinvention;

FIG. 2 illustrates a fluid processing system in accordance to anembodiment of the invention;

FIG. 3 illustrates a fluid processing system in accordance to anotherembodiment of the invention;

FIG. 4 illustrates a pump and a fluid reservoir in accordance to anembodiment of the invention;

FIG. 5 illustrates a pump and a fluid reservoir in accordance to anotherembodiment of the invention;

FIG. 6 illustrates a portion of a pump in accordance to an embodiment ofthe invention;

FIG. 7 illustrates a portion of a pump in accordance to anotherembodiment of the invention;

FIG. 8 illustrates a portion of a pump in accordance to yet anotherembodiment of the invention;

FIG. 9 illustrates a portion of a pump in accordance to yet anotherembodiment of the invention;

FIG. 10 illustrates a portion of a pump in accordance to yet anotherembodiment of the invention;

FIG. 11 illustrates a portion of a pump in accordance to yet anotherembodiment of the invention;

FIG. 12 illustrates a portion of a fluid processing system in accordanceto an embodiment of the invention;

FIG. 13 illustrates a portion of a fluid processing system in accordanceto another embodiment of the invention;

FIG. 14 illustrates a portion of a subsea system in accordance to anembodiment of the invention;

FIG. 15 illustrates a portion of a fluid processing system in accordanceto an embodiment of the invention; and

FIG. 16 illustrates a portion of a fluid processing system in accordanceto another embodiment of the invention.

DETAILED DESCRIPTION

Embodiments discussed herein disclose new subsea systems for efficientlymoving production fluids characterized by high gas volume fraction (GVF)from a hydrocarbon reservoir to a distant fluid storage facility.Specifically, the embodiments disclose an improved fluid processingsystem for effectively managing the GVF of the production fluids. Thefluid processing system of the present invention comprises a pump and afluid reservoir encompassing a portion of the pump. One or more slotsdefined in a casing of the pump, are configured to extract a portion ofa multiphase fluid flowing in the pump at an intermediate pressure. Theone or more slots may be defined in one or more regions of the casingand may have optimal shapes to facilitate extraction of a stagnantportion (flow) of the multiphase fluid without affecting a main flow ofthe multiphase fluid. A discharge device is coupled to a re-circulationconduit of the fluid reservoir. The discharge device may include oneamong a passive device and an active device to efficiently regulate thequantity of and the pressure at which a liquid phase of the multiphasefluid being fed to the pump for controlling the GVF of the productionfluids. Suitable discharge devices include valves and one or morecylinders comprising at least one hole or opening.

FIG. 1 represents a subsea system 100 for handling production fluidsdeployed in a subsea environment 102 proximate to a hydrocarbonreservoir 104. The hydrocarbon reservoir 104 may produce a productionfluid comprising oil, water, and gas. In certain embodiments, thehydrocarbon reservoir 104 may produce a production fluid comprising adry gas or crude oil and dry gas.

The subsea system 100 includes an inlet tank 106, a fluid processingsystem 108, a fluid re-circulation loop 110, and a fluid outlet 112. Thesubsea system 100 further includes a fluid inlet 114 in fluidcommunication with the inlet tank 106 coupled to the hydrocarbonreservoir 104, and a feed line 118 linking the fluid processing system108 to the inlet tank 106. In certain other embodiments, the fluid inlet114 may include a well-head valve (not shown in FIG. 1) for regulating aflow of a first production fluid stream 120 (i.e. production fluid) fromthe hydrocarbon reservoir 104. The inlet tank 106 is configured toreceive the production fluid stream 120 from the hydrocarbon reservoir104 and a primer liquid stream 123 from a pump outlet 124 of the fluidprocessing system 108 via the fluid re-circulation loop 110. In one ormore embodiments, the pump outlet 124 includes a liquid-gas separator(not shown in FIG. 1) configured to separate the primer liquid 123 froma compressed multiphase fluid 122. The primer liquid stream 123 may becomprised of a liquid stream of the compressed multiphase fluid 122. Theinlet tank 106 is configured to mix the production fluid stream 120 andprimer liquid stream 123 to produce thereby a second production fluidstream 126 (i.e. multiphase fluid) having a reduced gas volume fraction(GVF) relative to the production fluid 120. In one or more embodiments,the primer liquid 123 may include one or more liquids separated from themultiphase production fluid 126 such as water and crude oil. Inalternative embodiment, the primer liquid 123 may comprise an exogenousliquid such as a solvent (e.g. ethanol) or other liquid not derived fromthe multiphase production fluid 126.

The fluid processing system 108 includes a pump 128 and a fluidreservoir 130 encompassing at least a portion of the pump 128. The pump128 has a pump inlet 132, the pump outlet 124, and one or more slots 134defined in a casing 158 of the pump. The pump inlet 132 is fluidlycoupled to the inlet tank 106 and the pump outlet 124 is fluidly coupledto both the inlet tank 106 and to a distant storage facility 138. In theembodiment shown, the fluid-recirculation loop 110 has a flow-controlvalve 136 configured to regulate a flow of the primer liquid stream 123into the inlet tank 106. In certain other embodiments, the system 100may include a plurality of pumps 128 coupled in a parallel configurationor in a serial configuration. The fluid reservoir 130 has are-circulation conduit 140 disposed proximate to the pump inlet 132, are-injection conduit 142 disposed proximate to the one or more slots134, and a discharge device 144 coupled to the re-circulation conduit140. Pump 128 and fluid reservoir 130 are discussed in greater detailbelow.

The system 100 further includes a pipe 116 disposed between the fluidinlet 114 and distant storage facility 138. The pipe 116 has a by-passvalve 154 configured to regulate a flow of the production fluid stream120 from the hydrocarbon reservoir 104 to the distant storage facility138 based on one or more pre-determined conditions. In one or moreembodiments, the one or more pre-determined conditions may includestart-up, shutdown, and maintenance of the subsea system 100.

During operation inlet tank 106 receives and mixes the production fluidstream 120 from the hydrocarbon reservoir 104 with the primer liquidstream 123 from the pump outlet 124 to produce the multiphase fluid 126having a reduced GVF relative to the production fluid 120. Theproduction fluid stream 120 may include gas slugs 156 which, as noted,may harm system components or affect efficiency. The multiphase fluid126 is then fed to the fluid processing system 108.

The pump 128 receives the multiphase fluid stream 126 and increases itspressure. A portion of the multiphase fluid stream 126 flowing withinthe pump 128 at an intermediate pressure is extracted into the fluidreservoir 130 via the one or more slots 134.

In the fluid reservoir 130 the extracted portion of the multiphase fluid126 settles down and phase separates into an extracted liquid phase 146and extracted gaseous phase 148. In one or more embodiments, the fluidreservoir 130 itself is configured as a liquid-gas separator. In otherembodiments, the fluid reservoir 130 may include a discrete liquid-gasseparator. In such embodiments, the liquid-gas separator receives theextracted portion of the multiphase fluid 126 and separates the liquidphase from gaseous phase using, for example, a barrier, a filter, or avortex flow separator. In one or more embodiments, a suitable liquid-gasseparator may include one or more weir separators, filter separators,cyclone separators, sheet metal separators, or a combination of two ormore of the foregoing separators.

A portion of the extracted liquid phase 146 is re-circulated asindicated by a reference numeral 150, into the pump inlet 132 throughthe re-circulation conduit 140. In one or more embodiments, there-circulation of the extracted liquid phase 146 into the pump inlet 132is referred as an intermediate re-circulation. The discharge device 144regulates the flow of the extracted liquid phase 146 into the pump inlet132 where it is mixed with multiphase fluid 126 to further reduce theGVF of the multiphase fluid 126 being fed to the pump 128. The extractedgaseous phase 148 is re-injected as indicated by reference numeral 152,to the pump 128 through re-injection conduit 142. The re-injectionconduit 142 is shown as configured to deliver the gaseous phase 148upstream of the one or more slots 134. As noted pump 128 produces thecompressed multiphase fluid 122, a portion of which may be separated foruse as the primer liquid 123.

In one or more embodiments, the subsea system 100 may include aplurality of sensors (not shown in FIG. 1) coupled to an electroniccontrol unit (not shown in FIG. 1) for regulating the flow of the primerliquid stream 123 and/or the extracted liquid phase 146 and/or theproduction fluid stream 120. The plurality of sensors may include one ormore liquid-level indicators, flow meters, and speed sensors. Theelectronic control unit typically includes at least one data processor.The plurality of sensors may be configured to generate a plurality ofinput signals based on a plurality of sensed parameters of the subseasystem 100. The electronic control unit may be configured to generateone or more control signals based on the plurality of input signals.

In one embodiment, the electronic control unit generates a controlsignal to regulate feeding of the primer liquid stream 123 to the inlettank 106 via the flow control valve 136. The control unit may generate acontrol signal to regulate intermediate re-circulation of the portion ofextracted liquid phase 146 into the pump inlet 132 via the dischargedevice 144. The electronic control unit may be configured to regulatefeeding of the production fluid stream 120 to the distant storagefacility 138 via the by-pass valve 154.

FIG. 2 represents a fluid processing system 108 in accordance with anexemplary embodiment. The fluid processing system 108 includes a pump128 and a fluid reservoir 130. In the embodiments shown, the fluidreservoir 130 is an integral component of the pump 128. In certain otherembodiments, the fluid reservoir 130 may be a discrete component whichmay be fluidly coupled to the pump 128 via pipes.

Pump 128 has a shaft 160 disposed at least partially within a casing 158and coupled to a motor (not shown in FIG. 2), and one or more pumpstages 162. Each pump stage 162 has an impeller 164 and a diffuser 166.The pump 128 has one or more slots 134 such as through-holes, defined inthe casing 158. The one or more slots 134 are located proximate to apump inlet 132. In the embodiment shown, the one or more slots 134 arelocated after a second pump stage 162 b from the pump inlet 132. Eachslot 134 is positioned at about 20 percent to about 80 percent of alength “L” of the diffuser 166. In one or more embodiments, suitablepumps include rotary pumps, centrifugal pumps, and reciprocating pumps.

The re-injection conduit 142 is disposed between a first opening 174formed in a top portion 170 of the fluid reservoir 130 and a secondopening 176 formed in the casing 158. The re-circulation conduit 140 hasan opening 178 disposed proximate to the pump inlet 132. The opening 178is located at a bottom portion 172 of the fluid reservoir 130. There-circulation conduit 140 further includes the discharge device 144disposed at the opening 178. The one or more slots 134 and the dischargedevice 144 are discussed in greater detail below.

During operation multiphase fluid 126 is compressed at each pump stage162 via the impeller 164 and guided to a subsequent pump stage 162 viathe diffuser 166. The one or more slots 134 extract a portion of themultiphase fluid 126 at an intermediate pressure from the pump 128. Inthe illustrated embodiment, the extraction of the multiphase fluid 126is indicated by a reference numeral 180. The extracted multiphase fluid126 is separated into liquid phase and gaseous phase. As dictated bygravity, the extracted liquid phase 146 is stored at the bottom portion172 of the fluid reservoir 130 and the extracted gaseous phase 148 isstored at the top portion 170 of the fluid reservoir 130. The extractedgaseous phase 148 is re-injected to the pump 128 through there-injection conduit 142 wherein a portion of the extracted liquid phase146 is re-circulated to the pump 128 through the re-circulation conduit140. The discharge device 144 regulates the flow of the extracted liquidphase 146. In one or more embodiments, the re-circulation may depend onthe GVF at the pump inlet 132.

FIG. 3 represents a fluid processing system 108 in accordance withanother exemplary embodiment. The illustrated embodiment does notinclude a separate re-injection conduit 142 as shown in the embodimentof FIG. 2. One or more slots 134 defined in the casing 158 is configuredfor both extraction (as indicated by reference numeral 180) of themultiphase fluid 126 from the pump 128 and re-injection (as indicated byreference numeral 152) of the extracted gaseous phase 148 into the pump128. The extraction and re-injection may happen at the same pump stage162.

FIG. 4 represents a fluid processing system 108 comprising a pump 128and a fluid reservoir 130 in accordance with an exemplary embodiment.The pump 128 includes a first pump inlet 182 and a first pump outlet184. The pump 128 has a first set of pump stages 162 a and a second setof pump stages 162 b disposed within a casing 158. The first set of pumpstages 162 a is disposed between a pump inlet 132 and the first pumpoutlet 184. The second set of pump stages 162 b is disposed between thefirst pump inlet 182 and a pump outlet 124. The first pump inlet 184 andfirst pump outlet 182 are fluidly coupled to each other via a conduit186. The first and second set of pump stages 162 a and 162 b are in aserial configuration. The casing 158 further includes one or more slots134 disposed upstream relative to the first pump outlet 184. The fluidreservoir 130 encompasses the portion of the casing 158 defining thefirst set of pump stages 162 a.

During operation multiphase fluid 126 enters the first set of pumpstages 162 a where it is compressed to a first pressure. A portion ofthe multiphase fluid 126 at the first pressure is extracted through theone or more slots 134 into the fluid reservoir 130, as discussedearlier. In one or more embodiments, the first pressure may be anintermediate pressure. A remaining portion of the multiphase fluid 126substantially above the first pressure exits the first set of pumpstages 162 a through the first pump outlet 184 and flows in the conduit186 before being fed to the second set of pump stages 162 b via thefirst pump inlet 182. The multiphase fluid 126 is then compressed alongthe second set of pump stages 162 b to generate the compressedmultiphase fluid 122 at a second pressure. The pump outlet 124discharges the compressed multiphase fluid 122 from the pump 128.

FIG. 5 represents a fluid processing system 108 comprising a pump 128and a fluid reservoir 130 in accordance with an exemplary embodiment.The pump 128 includes a first pump inlet 132 a disposed at a first end188 of the pump 128 and a second pump inlet 132 b disposed at a secondend 190 opposite to the first end 188, of the pump 128. The pump 128 hasa first set of pump stages 162 a and a second set of pump stages 162 bdisposed within a casing 158. The first and second set of pump stages162 a and 162 b are in a parallel configuration. The pump outlet 124 isdisposed at an exit section of the first and second set of pump stages162 a and 162 b. The fluid reservoir 130 encompasses the portion of thecasing 158 defining the first set of pump stages 162 a. The bottomportion 172 of the fluid reservoir 130 further includes a liquid conduit192 fluidly coupled to the second fluid inlet 132 b. The liquid conduit192 includes a control valve 194. The top portion 170 of the fluidreservoir 130 includes a gaseous conduit 196 fluidly coupled to aportion of the casing 158 corresponding to the second set of pump stages162 b.

During operation multiphase fluid 126 enters the first and second set ofpump stages 162 a and 162 b of the pump 128. The multiphase fluid 126 iscompressed along the one or more stages of the first and second set ofpump stages 162 a and 162 b. A portion of the multiphase fluid 126flowing along the first set of pump stages 162 a is extracted into thefluid reservoir 130 through one or more slots 134 as discussed earlier.A remaining portion of the multiphase fluid 126 flowing along the firstset of pump stages 162 a and the multiphase fluid 126 flowing along thesecond set of pump stages 162 b are compressed to generate thecompressed multiphase fluid 122. The pump outlet 124 discharges thecompressed multiphase fluid 122 from the pump 128. In the embodimentshown, a portion of the extracted liquid phase 146 is fed from the fluidreservoir 130 into the second pump inlet 132 b via the liquid conduit192. The control valve 194 may regulate a flow of the portion of theextracted liquid phase 146. Further, a portion of the extracted gaseousphase 148 may be fed from the fluid reservoir 130 into the second set ofpump stages 162 b via the gaseous conduit 196.

FIG. 6 represents a portion 197 of a pump 128 in accordance with anexemplary embodiment. The portion 197 has a plurality of diffusers 166and a slot 134 defined in a casing 158. The slot 134 is positionedcorresponding to a mid-length of the plurality of diffusers 166 and hasa width “W₁”. Further, the slot 134 is a continuous slot having auniform size along the casing 158. In certain other embodiments, theslot 134 may be positioned anywhere between a leading edge 204 and atrailing edge 206 of the plurality of diffusers 166. Specifically, theslot 134 may be positioned at about 20 percent to about 80 percent ofthe length “L” of the plurality of diffusers 166. The slot 134 may beconfigured to extract a portion of the multiphase fluid 126 from thepump 128 and to re-inject an extracted gaseous phase 148 into the pump128.

FIG. 7 represents a portion 199 of a pump 128 in accordance with anotherexemplary embodiment. In the illustrated embodiment, a slot 134 definedin a casing 158 has a width “W₂” different than the width “W₁” as shownin the embodiment of FIG. 6. The slot 134 having a smaller width mayaccurately regulate a quantity of a multiphase fluid 126 extracted intothe fluid reservoir 130. Similar to the embodiment of FIG. 6, the slot134 is a continuous slot having a uniform size along the casing 158 andis positioned at a mid-length of a plurality of diffusers 166.

FIG. 8 represents a portion 201 of a pump 128 in accordance with yetanother exemplary embodiment. A slot 134 is located proximate to aleading edge 204 of a plurality of diffusers 166. Similar to theembodiment of FIG. 6, the slot 134 is a continuous slot having a uniformsize along a casing 158. FIG. 9 represents a portion 203 of a pump 128in accordance with yet another exemplary embodiment. A slot 134 islocated proximate to a trailing edge 206 of a plurality of diffusers166. Similar to the embodiment of FIG. 6, the slot 134 is a continuousslot having a uniform size along a casing 158.

FIG. 10 represents a portion of 205 of a pump 128 in accordance with yetanother exemplary embodiment. The portion 205 has one or more discreteslots 134 defined in a casing 158. In the illustrated embodiment, eachslot 134 is positioned corresponding to a mid-length of a plurality ofdiffusers 166. Further, each slot 134 has a width “W₁” and covers aportion of a pressure side 202 and a suction side 200 of at least onediffuser 166. As shown in the embodiments of FIGS. 6, 7, 8, and 9, eachslot 134 may have different width and may be positioned anywhere betweena leading edge 204 and a trailing edge 206 of the plurality of diffusers166.

FIG. 11 represents a portion of 207 of a pump 128 in accordance with yetanother exemplary embodiment. The portion 207 includes one or morediscrete slots 134 defined in a casing 158. In one embodiment, each slot134 is positioned proximate to a trailing edge 206. Each slot 134 has anon-uniform size along the casing 158 and is disposed between a suctionside 200 of a diffuser 166 and a pressure side 202 of a mutuallyadjacent diffuser 166. The shape and position of each slot 134 may bechosen such that an extraction of the multiphase fluid 126 happens froman area of the diffuser 166 where the multiphase fluid 126 tends tore-circulate (or have more turbulence or is a stagnant flow) within thepump 128. Each slot 134 removes the stagnant flow (i.e. low qualityflow) from such area of the diffuser 166 to improvise an aero dynamiceffect of the multiphase fluid 126 within the pump 128.

FIG. 12 represents a portion 208 of a fluid processing system 108 inaccordance with an exemplary embodiment. The portion 208 illustrates adischarge device 144 in accordance to the exemplary embodiment.

The discharge device 144 is an active device including a plurality ofconcentric cylinders 210 disposed at an opening 178 of there-circulation conduit 140. An outer concentric cylinder 210 a among theplurality of concentric cylinders 210 has a side wall 212 rotatablyengaged with an outer wall 214 of the re-circulation conduit 140.Similarly, an inner concentric cylinder 210 b among the plurality ofconcentric cylinders 210 has a side wall 216 coupled to a casing 158 ofa pump 128. The side walls 212 and 216 are inclined at a pre-determinedangle “a” relative to a wall 219 of a pump inlet 132. In one or moreembodiments, the pre-determined angle “a” may be a negative angle, apositive angle, zero, or combination thereof depending on an applicationand design criteria. The plurality of concentric cylinders 210 is ahollow cylinder with each cylinder 210 having one or more holes 218spaced apart from each other and disposed along a circumference of eachcylinder 210. The outer concentric cylinder 210 a is coupled to anactuator (not shown in FIG. 12) for rotating (as designated by areference number 217) the cylinder 210 a about an axis of the shaft 160.The inner concentric cylinder 210 b is a stationary cylinder. In certainother embodiments, the outer concentric cylinder 210 a may be stationaryand the inner concentric cylinder 210 b may be rotatable about the axisof the shaft 160.

During operation actuator may rotate the outer concentric cylinder 210 afor aligning one or more holes 218 a with one or more holes 218 b ofinner concentric cylinder 210 b. Such alignment of holes 218 a and 218 ballows the extracted liquid phase 146 to flow through the dischargedevice 144 into the pump inlet 132. The outer concentric cylinder 210 amay be regulated via the actuator by an electronic control unit asdiscussed in the embodiment of FIG. 1. The concentric cylinders 210 maycontrol a pressure and a quantity of the extracted liquid phase 146being re-circulated into the pump 128. In one or more embodiments,suitable actuators may include motors.

FIG. 13 represents a portion 209 of a fluid processing system 108 inaccordance with another exemplary embodiment. The portion 209illustrates a discharge device 144 in accordance to the exemplaryembodiment. The discharge device 144 is an active device including avalve 220 disposed in a pipe 222 which is coupled between are-circulation conduit 140 and a pump inlet 132. As discussed in theembodiment of FIG. 12, the valve 220 may be driven by an actuator toregulate intermediate re-circulation of an extracted liquid phase 146into the pump inlet 132.

FIG. 14 represents a portion 211 of a subsea system 100 in accordance toan exemplary embodiment. The portion 211 illustrates a discharge device144 and an actuator 225. The discharge device 144 is a passive deviceincluding a valve 224 disposed in a pipe 222 coupled to a re-circulationconduit 140 and a pump inlet 132. The actuator 225 is disposed in aconduit 232 coupled to a fluid outlet 112 and the pipe 222 via anopening 230. The actuator 225 is further coupled to the valve 224. Inthe embodiment shown, the actuator 225 is a first piston including aspring 234 disposed between a piston head (not labeled) and the opening230.

During operation a portion of a compressed multiphase fluid 122 flows inthe conduit 232 and a portion of an extracted liquid phase 146 flows inthe pipe 222. The first piston 225 is configured to reciprocate alongthe opening 230 to either engage or disengage the valve 224 based on apressure difference between the pipe 222 and conduit 232. For example,when a pressure applied by the compressed multiphase fluid 122 in theconduit 232 is significantly greater than a pressure applied by theextracted liquid phase 146 in the pipe 222, the first piston 225 engagesthe valve 224 and obstructs a flow of the extracted liquid phase 146into the pump inlet 132. Similarly, when the pressure applied by theextracted liquid phase 146 in the pipe 222 is significantly greater thanthe pressure applied by the compressed multiphase fluid 122 in theconduit 232, the first piston 225 disengages the valve 224 and allowsthe flow of the liquid phase 146 into the pump inlet 132.

In certain embodiments, the conduit 232 may further include a secondpiston (not shown in FIG. 14) disposed at an opening 113 formed in thefluid outlet 112. In such embodiments, the conduit 232 may be filledwith a fluid such as oil and water, different than the compressed fluid112. The second piston may compress the fluid based on the pressure ofthe compressed multiphase fluid 122 flowing in the fluid outlet 112 andthereby increase the pressure across the first piston 225 to engage thevalve 224.

FIG. 15 represents a portion 213 of a fluid processing system 108 inaccordance with yet another exemplary embodiment. The portion 213illustrates a discharge device 144 in accordance to the exemplaryembodiment. The discharge device 144 is a passive device including acylinder 236 disposed at an opening 178 of a re-circulation conduit 140.The cylinder 236 includes a side wall 240 coupled to a casing 158 and anouter wall 214 of a fluid reservoir 130. The side wall 240 is inclinedat a pre-determined angle “a” relative to a wall 219 of a pump inlet132. The cylinder 236 is a hollow cylinder with one or more holes 238spaced apart from each other and disposed along a circumference of thecylinder 236. In the embodiment shown, the cylinder 236 is a stationarycylinder. During operation an extracted liquid phase 146 isre-circulated continuously from the re-circulation conduit 140 into thepump inlet 132 via the one or more holes 238.

In certain embodiments, the side wall 240 is inclined at a zero anglerelative to the wall 219 i.e. the side wall 240 is disposedsubstantially parallel to the wall 219. In such embodiments, thecylinder 236 may move up and/or down via an actuator, to either openand/or close a portion of the holes 238 for selectively allowing theextracted liquid phase 146 to flow into the pump inlet 132.

FIG. 16 represents a portion 215 of a fluid processing system 108 inaccordance with yet another exemplary embodiment. The portion 215illustrates a discharge device 144 in accordance to the exemplaryembodiment. The discharge device 144 is a passive device including acylinder 242 disposed at an opening 178 of a fluid reservoir 130. Thecylinder 242 includes a hole 244 such as a slit, defined along acircumference of the cylinder 242. In the illustrated embodiment, thehole 244 is substantially perpendicular relative to a wall 219 of a pumpinlet 132. During operation an extracted liquid phase 146 isre-circulated from a re-circulation conduit 140 into the pump inlet 132via the hole 244.

Similar to the embodiment discussed in FIG. 15, the cylinder 242 maymove up and/or down via an actuator, to either open and/or close aportion of the slit 244 for selectively allowing the liquid phase 146 toflow into the pump inlet 132.

In accordance with certain embodiments discussed herein, a subsea systemfacilitates an efficient way of transporting a production fluidcharacterized by high gas volume fraction (gas slugs) from a subseahydrocarbon reservoir to a distant storage facility. In doing so, thesubsea system mixes a primer liquid with the production fluid primarilywithin an inlet tank to reduce a gas volume fraction (GVF) of theproduction fluid entering a pump and causing damage to the pump.Further, a fluid processing system of the present invention allowsextraction of a portion of the multiphase fluid at an intermediatepressure from the pump, separation of a gaseous phase from a liquidphase, and intermediate re-circulation of the extracted liquid phaseinto the pump to further reduce the GVF of the multiphase fluid at thepump inlet thereby avoiding the further damage to the pump. The processof re-circulation of the primer liquid and the intermediatere-circulation of the extracted liquid phase may be automated by havinga plurality of sensors and an electronic control unit.

While only certain features of embodiments have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedembodiments are intended to cover all such modifications and changes asfalling within the spirit of the invention.

1. A fluid processing system comprising: a pump including a casing, oneor more pump stages, a pump inlet, and a pump outlet, the casingdefining one or more slots, wherein at least one of the slots isconfigured to extract at least a portion of a multiphase fluid flowingwithin the pump, wherein each pump stage comprises a diffuser and animpeller; and a fluid reservoir encompassing at least a portion of thecasing and configured to receive and separate the portion of themultiphase fluid into an extracted liquid phase and an extracted gaseousphase, wherein the fluid reservoir comprises a re-circulation conduitdisposed proximate to the pump inlet, and a discharge device coupled tothe re-circulation conduit and configured to regulate re-circulation ofat least a portion of the extracted liquid phase to the pump via thepump inlet so as to reduce a gas volume fraction (GVF) of the multiphasefluid being fed to the pump.
 2. The system according to claim 1, whereinthe fluid reservoir further comprises a re-injection conduit coupled tothe one or more pump stages upstream relative to the slots andconfigured to regulate re-injection of the extracted gaseous phase intothe pump.
 3. The system according to claim 1, wherein the pump stagesare arranged in a serial configuration.
 4. The system according to claim1, wherein the pump stages are arranged in a parallel configuration. 5.The system according to claim 1, wherein the one or more slots arelocated at about 20 percent to about 80 percent of a length of thediffuser.
 6. The system according to claim 1, wherein the one or moreslots comprises at least one of a continuous slot, a discrete slot, anon-uniform slot.
 7. The system according to claim 6, wherein the one ormore slots are positioned along at least one of a mid-chord length ofthe diffuser, a leading edge of the diffuser, and a trailing edge of thediffuser.
 8. The system according to claim 1, wherein the dischargedevice comprises a plurality of concentric cylinders with each cylinderhaving one or more holes for allowing the extracted liquid phase to flowthrough the discharge device.
 9. The system according to claim 8,wherein each cylinder comprises a side wall inclined at a pre-determinedangle relative to the pump inlet, to regulate at least one a pressureand a quantity of extracted liquid phase being fed to the pump.
 10. Thesystem according to claim 1, wherein the discharge device comprises avalve disposed in a pipe coupled between the re-circulation conduit andthe pump inlet, for regulating a flow of the extracted liquid phase intothe pump.
 11. The system according to claim 1, wherein the dischargedevice comprises a valve disposed in a pipe and coupled to an actuatordisposed in a conduit, wherein the pipe is coupled to the re-circulationconduit and the pump inlet, and the conduit is coupled to the pipe andthe fluid outlet, wherein the valve is configured to regulate a flow ofthe extracted liquid phase into the pump based on a pressure differenceacross the pump.
 12. The system according to claim 1, wherein thedischarge device comprises a cylinder including one or more holes forallowing the extracted liquid phase to flow into the pump inlet.
 13. Thesystem according to claim 1, wherein the discharge device comprises atleast one of an active device and a passive device and configured toregulate a flow of the extracted liquid phase into the pump.
 14. Amethod comprising: introducing a multiphase fluid into a pump configuredto increase pressure of the multiphase fluid, wherein the pump comprisesa casing, one or more pump stages, a pump inlet, and a pump outlet,wherein each pump stage comprises a diffuser and an impeller; extractingat least a portion of the multiphase fluid flowing within the pump intoa fluid reservoir encompassing at least a portion of the casing via oneor more slots defined in the casing, wherein the fluid reservoircomprises a re-circulation conduit disposed proximate to the pump inletand a discharge device coupled to the re-circulation conduit; separatingthe portion of the multiphase fluid into an extracted liquid phase andan extracted gaseous phase; re-circulating at least a portion of theextracted liquid phase through the re-circulation conduit into the pumpvia the pump inlet by regulating a flow of the extracted liquid phasevia the discharge device; and mixing the extracted liquid phase with themultiphase fluid at the pump inlet so as to reduce the gas volumefraction (GVF) of the multiphase fluid being fed to the pump.
 15. Themethod of claim 14, further comprising re-injecting the extractedgaseous phase into the one or more pump stages upstream relative to theslots via the re-injection conduit coupled to the fluid reservoir. 16.The method of claim 14, wherein the regulating comprises controlling thedischarge device having a plurality of concentric cylinders and one ormore holes disposed on each cylinder, for allowing a flow of theextracted liquid phase into the pump.
 17. The method of claim 14,wherein the regulating comprises controlling the discharge device havinga valve disposed in a pipe coupled between the re-circulation conduitand the pump inlet, for allowing a flow of the extracted liquid phaseinto the pump.
 18. The method of claim 14, wherein the regulatingcomprises controlling the discharge device having a valve coupled to anactuator, for allowing a flow of the extracted liquid phase into thepump based on a pressure difference across the pump, wherein the valveis disposed in a pipe and the actuator is disposed in a conduit, whereinthe pipe is coupled to the re-circulation conduit and the pump inlet,and the conduit is coupled to the pipe and the fluid outlet.
 19. Amethod comprising: receiving a first production fluid in an inlet tankand mixing it with a primer liquid to produce thereby a secondproduction fluid (multiphase fluid) having a reduced gas volume fraction(GVF) relative to the first production fluid; introducing the multiphasefluid from the inlet tank into a pump configured to increase pressure ofthe multiphase fluid and produce thereby a compressed multiphase fluid,wherein the pump comprises a casing, one or more pump stages, a pumpinlet, and a pump outlet, wherein each pump stage comprises a diffuserand an impeller; extracting at least a portion of the multiphase fluidflowing within the pump into a fluid reservoir encompassing at least aportion of the casing via one or more slots defined in the casing,wherein the fluid reservoir comprises a re-circulation conduit disposedproximate to the pump inlet and a discharge device coupled to there-circulation conduit; separating the portion of the multiphase fluidinto an extracted liquid phase and an extracted gaseous phase;re-circulating at least a portion of the extracted liquid phase throughthe re-circulation conduit into the pump via the pump inlet byregulating a flow of the extracted liquid phase via the dischargedevice; mixing the extracted liquid phase with the multiphase fluid atthe pump inlet to further reduce the GVF of the multiphase fluid beingfed to the pump; and transporting the compressed multiphase fluid fromthe pump to a fluid storage facility via a fluid conduit.
 20. The methodaccording to claim 19, further comprising re-injecting the extractedgaseous phase into the one or more pump stages upstream relative to theone or more slots via the re-injection conduit coupled to the fluidreservoir.
 21. The method according to claim 19, wherein the primerliquid comprises a liquid stream of the compressed multiphase fluid,which is delivered to the inlet tank via a re-circulation loop coupledto the fluid conduit, wherein the re-circulation loop comprises acontrol valve configured to regulate a flow of the liquid stream.